Regarding her trip to the city and the possibility she could meet with the OM, do the two of you have a plan as to now she can avoid these types of opportunities that could tempt her to break her NC with the OM?

It is comparable to affair proofing your M. For a couple to believe their M is so strong that there is no need for an affair-proof plan, is very unwise. Even if there has never been any hint of looking at another person, a couple should agree upon certain actions being in place that assures the M will be void of infidelity. With that said, whenever there has been any type of an A in a M, you want to reinforce support back to a healthy relationship again.

Are the two of you discussing ways to give her support whenever there could be obvious opportunity to contact her OM?

It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!